1. Field of the Invention
The present invention relates to the technical field of combustion chambers for gas turbine engines. It is aimed in particular at the chamber end wall. Finally, it relates to a gas turbine engine such as a turbojet engine equipped with such a combustion chamber.
2. Description of the Related Art
In all that follows, the terms “axial”, “radial”, “transverse” correspond respectively to an axial direction, a radial direction and a transverse plane of the engine, and the terms “upstream” and “downstream” correspond respectively to the direction in which the gases flow through the engine.
A conventional divergent combustion chamber is illustrated in FIG. 1 which is an axial section showing half of the combustion chamber, the other half thereof being its symmetric counterpart with respect to the axis of the engine (not depicted). The combustion chamber 110 is housed downstream of a diffusion chamber 130 which is an annular space defined between an external casing 132 and an internal casing 134, into which a compressed oxidizing agent, ambient air, originating upstream from a compressor (not depicted) is introduced via an annular diffusion duct 136.
This divergent combustion chamber 110 comprises two concentric walls: an external wall 112 and an internal wall 114, which are coaxial and substantially conical. The walls widen from the upstream to downstream direction. The external 112 and internal 114 walls of the combustion chamber 110 are joined together, toward the upstream side of the combustion chamber, by a chamber end wall 116.
The chamber end wall 116 is a frustoconical annular component which extends between two substantially transverse planes widening from the downstream to upstream direction. The chamber end wall 116 is connected to each of the two, external 112 and internal 114, walls of the combustion chamber 110. The chamber end wall 116 has a small cone angle. It is provided with injection systems 118 through which the injectors 120, which introduce fuel into the upstream end of the combustion chamber 110 where the combustion reactions take place, pass.
The effect of these combustion reactions is to radiate heat from the downstream to upstream direction toward the chamber end wall 116. Thus, during operation, the chamber end wall is subjected to high temperatures. To protect it, segmented heat shields, also known as deflectors 122, are inserted between the site of combustion and the chamber end walls. These deflectors 122, one of which is depicted in FIG. 2, are substantially flat plates welded to the chamber end wall 116 with a central opening 122a for the passage of the injector. They comprise two lateral baffles 122b, 122c along the radial edges facing toward the chamber end wall and two tongues for guiding air along the transverse edges facing toward the site of combustion and creating a space with respect to the respective internal and external walls 114 and 112 of the chamber. The deflectors are cooled by jets of cooling air entering the combustion chamber 110 through cooling orifices 124 pierced in the chamber end wall 116 impinging on them. The air of which these jets are formed, flowing from the upstream direction downstream, is guided by streamlining of the chamber 126, passing through the chamber end wall 116 through the cooling orifices, and impinges on the upstream face of the deflectors 122. The air is then guided radially toward the inside and the outside of the site of combustion to begin to form the film that cools the walls 114 and 112 respectively.
This guidance along the deflectors is performed by the radially directed lateral baffles. These baffles also perform a sealing function. Being in contact with or creating a minimal gap with respect to the chamber end wall, they prevent the air from infiltrating between two adjacent deflectors, from entering the site of combustion and from disrupting combustion. Such disturbances would have an impact on pollution and are therefore to be avoided. What would happen in fact would be that the performance in terms of the emissions of CO and CHx pollutants would be liable to be degraded through the unwanted ingress of this cold air, particularly at engine idling speeds at which the clearance gap is larger.
Current evolutions in the means of supplying the chamber with air and with fuel have led to the production of injection systems which are increasingly difficult to incorporate into the chamber end wall. For example, multipoint injection systems are of increasing diameter because a substantial part of the air admitted to the chamber passes through them; they therefore occupy an increasing amount of space on the periphery of the chamber end wall, leaving an ever smaller gap between two adjacent systems.
A similar situation is encountered when the number of injection systems needs to be increased for the same chamber with a view to reducing dead regions between two adjacent injectors or alternatively when the dimensions of the chamber end wall are reduced for the same number of injection systems.
It then follows that, in such instances, the deflector centering openings are close together. There is therefore very little space to form lateral baffles on the deflectors.
FIGS. 3 and 4 show two solutions that could be imagined by applying the prior art to a situation such as this. Thus, in FIG. 3, the deflector 222 has a baffle 222b, 222c on each side of the lateral edges which occupies the entire region B, C between the edge of the deflector and the flange 222a′ that forms the edge of the opening 222a. This solution would maintain sealing but, because of this additional thickness, the deflector would not be able to be cooled in this region.
In FIG. 4, the solution is to interrupt the baffle 322b, 322c in the critical region between the lateral edges of the deflector 322 and the flange 322a′ on the edge of the opening 322a. The space created allows the deflector to be cooled by impingement of air jets, but at the expense of sealing.